With the continuous advancement of industrialization, the problem of air pollution has become increasingly prominent. How to overcome the key problems such as low efficiency and difficult recovery of industrial waste gas purification, and use new technologies and new materials to win the "blue sky defense war"?
The project "Creation and Application of Gas Purification Membrane Materials" developed by the team of Jin Wanqin, a professor at the School of Chemical Engineering and the National Key Laboratory of Materials Chemical Engineering of Nanjing University of Technology, provides an effective solution to the above problems. They have developed the world's first organic-inorganic composite membrane and biphobic membrane products, and realized the large-scale application of membrane technology in the fields of chlorine-containing gas and oily smoke treatment, and recently won the second prize of the 2023 National Science and Technology Progress Award.
Focus on air pollution control and carry out research on gas purification membrane technology
"The development of high-efficiency and energy-saving gas purification and recovery technology is a key issue that needs to be solved urgently in the current air pollution control, and it is also an important task that our scientific and technological workers must shoulder." Jin Wanqin introduced that the composition of industrial waste gas in the petrochemical and pharmaceutical fields is complex, among which chlorine-containing organic volatiles, super-subdivision and oily gas are extremely difficult to treat, and the existing technologies such as cyclone, electrostatic and bag dust removal often have problems such as low treatment efficiency and unstable operation. Compared with traditional gas purification technology, membrane technology has the characteristics of high efficiency and low energy consumption, and is expected to achieve standard emission and resource reuse at the same time.
Until then, membrane technology had been widely used in the field of liquid separation. Under the guidance of Professor Xu Nanping, an academician of the Chinese Academy of Engineering, and led by Professor Xing Weihong, the scientific research team of Nanjing University of Technology completed the zero discharge technology and demonstration project of membrane pulping wastewater in the project of "Membrane Preparation and Integration Technology for Zero Discharge of Pulping Wastewater", which has reborn the 10 billion yuan project of Nantong Prince Papermaking, which has been in a desperate situation. This makes Jin Wanqin more convinced that membrane technology will also be able to "show its talents" in the field of gas purification.
"Previously, the gas purification membrane materials on the market had problems such as low separation performance, difficult large-scale preparation, and unstable operation." Jin Wanqin said that the existing membrane materials are difficult to cope with complex working conditions such as large emission volume per unit time of industrial flue gas and small filtration driving force.
To this end, he led the team to focus on the common problems faced by industrial waste gas purification and recovery, and carried out systematic and in-depth research on the bottleneck problem of gas purification membrane technology.
Create organic-inorganic composite membranes to achieve a leap in the performance of gas purification membranes
Dedicated to deep cultivation to break the wall, twenty years of sharpening the sword to show the edge. Jin Wanqin led the team to find a new type of membrane - organic-inorganic composite membrane. Why do you want to make two materials stacked? Jin Wanqin said that this can better play the advantages of the two materials. By designing a rigid inorganic support and an organic film layer to construct a new structure of the confined swelling interface, the team successfully broke through the limitation of membrane flux and selectivity and solved the instability of the organic film layer due to swelling in organic solvents.
"The project constructs a theoretical framework for the design and preparation of organic-inorganic composite membranes, and provides a theoretical and technical basis for the preparation and application of membrane amplification." Jin Wanqin said that in the process of research, the team discovered the interfacial limited swelling mechanism and interlayer interlayer interfacial resistance effect of composite membranes, and successfully broke through the limitations of membrane flux, selectivity and stability through innovative design, and achieved a performance leap in gas purification membrane technology.
In addition, they also overcome the problem of organic solvent intolerance of existing membrane materials, breaking the bottleneck of traditional membrane permeability and selectivity. The wettability and interfacial bonding of the membrane surface were regulated in an orderly manner, and the organic-inorganic composite membrane and biphobic membrane products were developed through the activation grafting modification technology, which significantly improved the anti-fouling performance and long-term service performance of the membrane.
"Isn't this film just coated with an organic layer of inorganic material? Is it really that hard?" In the face of doubts, Jin Wanqin said that the difficulty of this kind of film lies in how to solve the interface bond between the inorganic layer and the organic layer, which involves how to control the thickness of the film layer, the roughness of the support, the viscosity of the polymer solution, and how to ensure the integrity of the film layer in the amplification preparation process...... These require the team to refine through trial and error.
Break through the bottleneck of large-scale preparation and apply it in more than 200 sets of projects
"From the initial 5 cm long sample in the laboratory to the current 80 cm long product, it took us 10 years to realize the gas purification membrane material from the laboratory to the pilot test." At the State Key Laboratory of Materials Chemical Engineering at Nanjing University of Technology, Jin Wanqin demonstrated this gas purification membrane with a thickness of no more than 5 microns. In the process, he led the team to overcome the large-scale preparation problem of gas purification membrane technology. Since 2014, the organic-inorganic composite membrane product has officially entered the market.
In view of the international problem that oily aerosols in industrial flue gas are easy to adsorb and form a pollution layer on the surface of the filter media, which affects the membrane structure and air permeability, the team proposed a heat-assisted in-situ functionalization method for surface hydrophobic and oleophobic modification, which realized the orderly regulation of membrane interface adhesion and surface wettability, and created a biphobic gas purification membrane material, which significantly improved the anti-pollution performance and long-term service performance of the membrane.
"Compared with the international advanced technology, the air permeability rate of our gas purification membrane products is increased by more than 30%, the mechanical properties are increased by 198%, and the removal rate of 0.3 micron ultrafine dust far exceeds the international standard, reaching more than 99.99%." Talking about the double permeable film, Professor Zhong Zhaoxiang, the second completer of the award-winning project, said that the adsorption force of pollutants such as oily aerosols in the flue gas on the surface of the double permeable film is small, and the polluted layer is easy to detach from the membrane surface under the action of external forces such as gravity and backflushing, so as to have a self-cleaning effect, which provides a new way to solve the application of membrane materials in high-viscosity and high-humidity systems, and the stable operation life of the membrane is also extended by more than 3 times.
At present, the gas purification membrane technology has been applied in more than 200 sets of projects such as Sinopec and Hengyi Petrochemical, with a cumulative treatment of more than 300 billion cubic meters of industrial gases and a new recovery value of more than 1 billion yuan of high value-added powder and organic solvent.
"One membrane cannot solve all problems, which also puts forward higher requirements for our scientific research work." Jin Wanqin said that in the next step, the team will continue to work hard to improve the separation performance and applicability of gas purification membrane materials, innovate and develop a new type of hybrid matrix membrane, and hope to achieve large-scale preparation in the next 1 to 2 years.
Author: Yang Fang Zhu Lin
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